A well-known technique for producing heterostructures by layer transfer is the SMART CUT® technique. A particular example of implementing the SMART CUT® technique is described in U.S. Pat. No. 5,374,564 or in the article by A. J. Auberton-Hervé et al. entitled “Why can Smart-Cut change the future of microelectronics?,” Int. Journal of High Speed Electronics and Systems, vol. 10, No. 1, 2000, pp. 131-146. That technique employs the following steps:                a) bombarding one face of a donor substrate (for example, formed from silicon) with light ions of the hydrogen or rare gas type (for example, hydrogen and/or helium) to implant those ions in sufficient concentration into the substrate; the implanted zone creates a layer of weakness by forming microcavities or platelets during splitting annealing;        b) bringing that face of the donor substrate into intimate contact (bonding) with a receiving substrate; and        c) splitting annealing, whereby the effect of a crystalline rearrangement and pressure in the microcavities or platelets formed from the implanted species causes fracture or cleavage at the implanted layer in order to obtain a heterostructure resulting from transfer of the layer of donor substrate onto the receiving substrate.        
However, the heterostuctures obtained thereby exhibit defects, not only at the surface of the transferred layer but also at the interfaces of the layers constituting the heterostructure.
Various types of surface defects may appear after transferring a layer onto a receiving substrate. Such defects include: surface roughness, non-transferred zones (NTZ), blisters, voids, or voids of the COV (crystal-orientated void) type, etc.
Such defects have diverse origins, such as poor transfer, the presence of subjacent defects in the various layers of the structure, the quality of bonding at the interfaces or simply the various steps that have to be carried out in order to fabricate such structures (implantation of species, heat treatment, etc.).
In order to overcome those problems, various techniques have been developed such as, for example, low temperature annealing (in particular, as described in U.S. Patent Application No. 2006/0040470), plasma treatments that can increase bonding energies at the interfaces and result in splitting of the layer to be transferred with few defects. It is known that during a transfer, the higher the bonding energy between the donor substrate and the receiving substrate, the fewer will be the defects in the resulting heterostructure. The solutions developed, such as plasma treatment of the surface or surfaces to be bonded, are used to reinforce the bonding energy while limiting the temperature of the heat treatment applied for splitting, in order to limit the diffusion of contaminants.
Similarly, JP 2005/085964 proposes reinforcing the bonding energy before splitting the layer to be transferred by using a helium implantation step and then applying a splitting anneal at high temperature in ranges from 800° C. to 1100° C.
Another method, presented in U.S. Pat. No. 6,756,286, is intended to improve the surface quality of the transferred layer after splitting it. That method comprises forming a zone of inclusions to confine the gaseous species derived from implantation in order to reduce the surface roughness of the split layer by reducing the implantation doses and the thermal budget.
Finally, U.S. Pat. No. 6,828,216 proposes applying splitting annealing in two phases, the first phase being used to accomplish the start of unbonding of the layer to be transferred in a standard range of 400° C. to 500° C., and the second phase being used to finish unbonding with a view to obtaining a good quality surface with temperatures at the end of the anneal of approximately 600° C. to 800° C.
However, those current techniques are not suitable for all SeOI (semiconductor-on-insulator) type heterostructures, in particular, those comprising a thin buried oxide layer (UTBOX, “Ultra Thin Buried OXide layer”) or even containing no oxide layer, such as heterostructures of the DSB (direct silicon bonding) type.
In fact, with this type of heterostructure, since the oxide layer is thin or non-existent, the diffusing species (for example, gases) are not trapped in the thickness of the oxide layer and may be the source of many defects within the heterostructure.